This invention relates to the field of electric motor control and more particularly to apparatus and method for limiting high current flows associated with excessive torque conditions. The invention has particular application to a drive motor for a windshield wiper but finds utility in other motors connected for driving a load along a repeating path. In cases wherein movement of the load is temporarily blocked by an obstruction, such as ice or crusted snow on a windshield, the motor may exert excess torque in an attempt to clear the blockage. This may lead to excess current flow and consequent damage to the motor.
Contemporary windshield wiper systems require drive motors able to deliver a wide range of speeds and torques. When operating at lower speeds and higher torques the motor is generally outside its operating region of maximum efficiency. Under such operating conditions the motor easily overheats, thereby increasing armature resistance, further raising the heat and the current flow until a circuit breaker disengages or the motor burns up.
It is a principal object of this invention to limit the current flow to an electric drive motor in such a manner as to deal effectively with conditions of high torque requirements without suffering damage in the process.